1. Field of the Invention
The present invention relates to methods and apparatus of probabilistically classifying tissue in vivo and in vitro using fluorescence spectroscopy, and more particularly to probabilistically classifying normal, cancerous and precancerous epithelial tissue such as cervical tissue in vivo and in vitro using fluorescence spectroscopy.
2. Description of Related Art
Fluorescence, infrared absorption and Raman spectroscopies have been proposed for cancer and precancer diagnosis. Many groups have successfully demonstrated their use in various organ systems. Auto and dye induced fluorescence have shown promise in recognizing atherosclerosis and various types of cancers and precancers. Many groups have demonstrated that autofluorescence may be used for differentiation of normal and abnormal tissues in the human breast and lung, bronchus and gastrointestinal tract. Fluorescence spectroscopic techniques have also been investigated for improved detection of cervical dysplasia.
Although a complete understanding of the quantitative information contained within a tissue fluorescence spectrum has not been achieved, many groups have applied fluorescence spectroscopy for real-time, non-invasive, automated characterization of tissue pathology. Characterization of tissue pathology using auto-fluorescence, see Appendix A, References 10-23, as well as photosensitizer induced fluorescence, see Appendix A, References 25-27, to discriminate between diseased and non-diseased human tissues in vitro and in vivo has been described in a variety of tissues. However, these various approaches have not been entirely satisfactory.
Auto-fluorescence spectra of normal tissue, intraepithelial neoplasia and invasive carcinoma have been measured from several organ sites in vivo. For example, in vivo studies of the human colon at 370 nm excitation (Appendix A, Reference 13) indicated that a simple algorithm based on fluorescence intensity at two emission wavelengths can be used to differentiate normal colon and adenomatous polyps with a sensitivity and specificity of 100% and 97%, respectively. Shomacker et al. (Appendix A, Reference 14) conducted similar studies in vivo at 337 nm excitation and demonstrated that a multivariate linear regression algorithm based on laser induced fluorescence spectra can be used to discriminate between normal colon and colonic polyps with a similarly high sensitivity and specificity. Lam et al. developed a bronchoscope which illuminates tissue at 442 nm excitation and produces a false color image in near real-time which represents the ratio of fluorescence intensities at 520 nm (green) and 690 nm (red) (Appendix A, References 16 and 17). In vivo studies demonstrated that the ratio of red to green auto-fluorescence is greater in normal bronchial tissues than in abnormal bronchial tissues (Appendix A, Reference 16). In a trial with 53 patients, the sensitivity of fluorescence bronchoscopy was found to be 72%, as compared to 50% for conventional white light bronchoscopy (Appendix A, Reference B 17).
Nonetheless, a reliable diagnostic method and apparatus with improved diagnostic capability for use in vitro and in vivo is needed to allow faster, more effective patient management and potentially further reduce mortality.